This is most common in farmponds and small lakes with few springs and dependent on inlets and outlets for fresh water. It can happen in years with thick milky ice or
heavy snow where the light and oxygen can't penetrate to the fish. There will be dead fish floating come spring. I saw it firsthand on a small SE Mi lake one winter when two snowmobile clubs showed up and decided to make this mile long lake their homebase. They packed down every inch of snow so tight that no light or oxygen got through and in the spring their were dead fish everywhere. Not a concern in this iceless year.
Ted
